Traction control system for fourwheel drive vehicle

Abstract

A traction control system for a fourwheel drive vehicle having a center differential comprises a brake pressure control apparatus, an engine output control apparatus, a differential limiting torque control apparatus, vehicle speed calculating means for calculating a reference vehicle speed of a vehicle, slip amount calculating means for calculating a slip amount of each wheel, target slip amount determining means for determining a front target slip amount of front wheels and a rear target slip amount of rear wheels, traction control determining means for determining to operate a traction control when the slip amount of the front wheels exceeds the front target slip amount or when the slip amount of the rear wheels exceeds the rear target slip amount, brake pressure calculating means for calculating a brake pressure so as to apply a brake to the wheels and engine output calculating means for calculating a target engine torque corresponding to a difference between the slip amount and the target slip amount, whereby driving force and side force of the vehicle is properly controlled and the vehicle can be prevented from spins under any driving conditions.

What is claimed is: 
     
       1. A traction control system of a fourwheel drive vehicle having an engine, a transmission, front wheels, rear wheels, a center differential for dividing a torque into said front and rear wheels, a front differential, a rear differential, front left and right wheels, a wheel speed sensor for detecting a wheel speed of each wheel of said front and rear wheels, a longitudinal acceleration sensor for detecting a longitudinal acceleration of said vehicle, a brake pressure control apparatus for independently controlling a brake pressure on said each wheel, an engine output control apparatus for controlling an output of said engine and a control unit for controlling said brake pressure control apparatus and said engine output control apparatus, comprising: vehicle speed calculating means provided in said control unit for calculating a reference vehicle speed of said vehicle based on a lowest wheel speed in said wheels and said longitudinal acceleration;   slip amount calculating means provided in said control unit for calculating a slip amount of said each wheel based on said reference vehicle speed and said wheel speed of said each wheel;   target slip amount determining means provided in said control unit for determining a front target slip amount of said front wheels and a rear target slip amount of said rear wheels according to said reference vehicle speed;   traction control determining means provided in said control unit for determining to operate a traction control when said slip amount of said front wheels exceeds said front target slip amount or when said slip amount of said rear wheels exceeds said rear target slip amount and for outputting a traction control signal;   brake pressure calculating means provided in said control unit responsive to said traction control signal for calculating a brake pressure corresponding to a difference between said slip amount and said target slip amount and for outputting a brake pressure signal to said brake pressure control apparatus so as to apply a brake to said wheels; and   engine output calculating means provided in said control unit responsive to said traction control signal for calculating a target engine torque corresponding to a difference between said slip amount and said target slip amount and for outputting a target engine torque signal to said engine output control apparatus.   
     
     
       2. The traction control system according to claim 1, further comprising: tire chain detecting means provided in said control unit for detecting tire chain wearing wheels and tire chain not-wearing wheels based on said wheel speed of said each wheel and for outputting a tire chain wearing signal; and   target slip amount correcting means provided in said control unit responsive to said tire chain wearing signal for correcting said target slip amounts of said target slip amount determining means so as to increase the target slip amount of said tire chain wearing wheels and to reduce the target slip amount of said tire chain not-wearing wheels.   
     
     
       3. The traction control system according to claim 1, further comprising: a steering wheel angle detecting means for detecting a steering wheel angle;   tire chain detecting means provided in said control unit for detecting tire chain wearing wheels and tire chain not-wearing wheels based on said wheel speed of said each wheel and said steering wheel angle and for outputting a tire chain wearing signal; and   target slip amount correcting means provided in said control unit responsive to said tire chain wearing signal for correcting said target slip amounts of said target slip amount determining means so as to increase the target slip amount of said tire chain wearing wheels and to reduce the target slip amount of said tire chain not-wearing wheels.   
     
     
       4. A traction control system of a fourwheel drive vehicle having an engine, a transmission, front wheels, rear wheels, a center differential for dividing a torque into said front and rear wheels, a differential limiting mechanism for producing a differential limiting torque between said front and rear wheels, a differential limiting torque control apparatus for controlling said differential limiting mechanism, a front differential, a rear differential, front left and right wheels, a wheel speed sensor for detecting a wheel speed of each wheel of said front and rear wheels, a longitudinal acceleration sensor for detecting a longitudinal acceleration of said vehicle, a brake pressure control apparatus for independently controlling a brake pressure on said each wheel, an engine output control apparatus for controlling an output of said engine and a control unit for controlling said brake pressure control apparatus and said engine output control apparatus, comprising: vehicle speed calculating means provided in said control unit for calculating a reference vehicle speed of said vehicle based on a lowest wheel speed in said wheels and said longitudinal acceleration;   slip amount calculating means provided in said control unit for calculating a slip amount of said each wheel based on said reference vehicle speed and said wheel speed of said each wheel;   target slip amount determining means provided in said control unit for determining a front target slip amount of said front wheels and a rear target slip amount of said rear wheels according to said reference vehicle speed;   traction control determining means provided in said control unit for determining to operate a traction control when said slip amount of said front wheels exceeds said front target slip amount or when said slip amount of said rear wheels exceeds said rear target slip amount and for outputting a traction control signal;   brake pressure calculating means provided in said control unit responsive to said traction control signal for calculating a brake pressure corresponding to a difference between said slip amount and said target slip amount, for outputting a brake pressure signal to said brake pressure control apparatus so as to apply a brake to said wheels and for outputting a signal to nullify said differential limiting torque to said differential limiting torque control apparatus; and   engine output calculating means provided in said control unit responsive to said traction control signal for calculating a target engine torque corresponding to a difference between said slip amount and said target slip amount and for outputting a target engine torque signal to said engine output control apparatus.   
     
     
       5. The traction control system according to claim 4, further comprising: tire chain detecting means provided in said control unit for detecting tire chain wearing wheels and tire chain not-wearing wheels based on said wheel speed of said each wheel and for outputting a tire chain wearing signal; and   target slip amount correcting means provided in said control unit responsive to said tire chain wearing signal for correcting said target slip amounts of said target slip amount determining means so as to increase the target slip amount of said tire chain wearing wheels and to reduce the target slip amount of said tire chain not-wearing wheels.   
     
     
       6. The traction control system according to claim 4, further comprising: a steering wheel angle detecting means for detecting a steering wheel angle;   tire chain detecting means provided in said control unit for detecting tire chain wearing wheels and tire chain not-wearing wheels based on said wheel speed of said each wheel and said steering wheel angle and for outputting a tire chain wearing signal; and   target slip amount correcting means provided in said control unit responsive to said tire chain wearing signal for correcting said target slip amounts of said target slip amount determining means so as to increase the target slip amount of said tire chain wearing wheels and to reduce the target slip amount of said tire chain not-wearing wheels.